The present disclosure relates to systems and methods for wireless magnetic tracking, which may be used, by way of example, during radiation therapy. Radiation therapy is an effective therapeutic modality for combating malignant tumors. During external beam radiation therapy, an external source of ionizing radiation is used to irradiate cancerous cells. Intensity-Modulated Radiation Therapy (“IMRT”) is one form of external beam radiation therapy in which the ionizing radiation is broken into many pencil-thin beams using a multi-leaf collimator. During IMRT, these pencil-thin beams enter the body from various angles and conform to the shape of a tumor, thereby reducing irradiation of (and, hence, damage to) surrounding healthy tissues. Accurate, real-time knowledge of the position and orientation of the tumor is needed to maximize the dosage of radiation to cancerous cells while minimizing the dosage of radiation to surrounding healthy cells. Respiration, circulation, and/or peristalsis, however, often cause movement of a patient's organs and, thus, the tumor during radiation therapy.
Several magnetic tracking systems have been utilized to estimate the position of a tumor during radiation therapy. Generally, these systems include a transponder that is implanted in or near the tumor and has one or more magnetic sensors for measuring the strength of a magnetic field generated by excitation coils located near the patient. Mapping the strength and direction of the generated magnetic field at the location of the transponder allows the position of the tumor to be tracked. Many existing wireless magnetic tracking systems use passive transponders, which require temporally separated excitation and measurement periods. The inability to gather position data during excitation of the magnetic sensors in passive transponders slows down the tracking speed of such systems. Furthermore, existing wireless magnetic tracking systems typically use a large number of excitation coils, which further slows down their tracking speeds.